Bleach solution for use in the process of color photography containing an alkali metal fluoride

ABSTRACT

A BLEACH SOLUTION FOR USE IN THE PROCESS OF COLOR PHOTOGRAPHY CONTAINING AN ALKALI METAL FLUORIDE WHICH PREVENTS THE FORMATION OF BLUE DYE DEPOSITS ON COLOR FILM AND COLOR PAPER.

3,806,343 BLEACH SOLUTION FOR USE IN THE PROCESS OF COLOR PHOTOGRAPHY CONTAINING AN ALKALI METAL FLUORIDE Frederick, William Millard, Montrose, Pa., and William Le Roy Wike, Endicott, N.Y., assignors to GAF Corporation, New York, N.Y. No Drawing. Filed May 23, 1972, Ser. No. 256,160 Int. Cl. G03c 5/32, 7/00, 7/16 US. CI. 96-60 R 9 Claims ABSTRACT OF THE DISCLOSURE A bleach solution for use in the process of color photography containing an alkali metal fluoride which prevents the formation of blue dye deposits on color film and color paper.

This invention relates to photographic bleaching baths. More particularly, this invention relates to solutions used in bleaching the silver image in a multi-color film or paper following color-forming development.

It is known that in the processing of multi-color photographic film or paper, the silver formed in all the layers during development is converted into a silver salt by any of the well-known bleach solutions which commonly containan alkali metal ferricyanide as the oxidizing agent, a buffer mixture, accelerators, corrosion inhibitors, and in most instances either potassium bromide, sodium bromide or sodium chloride. The silver salt thus formed is then removed by dissolving it in a silver salt solvent such as hypo.

It has been observed that with the conventional bleach bath containing an alkali metal ferricyanide, such as p0- tassium ferricyanide, used in processing color films and color paper materials a reaction takes place which results in the deposit of blue dye, for example Prussian Blue, which ultimately adheres to transparencies and prints in the bath. In addition, in cine machine processing, the blue dye formation results in the corrosion of the rollers used to transport the film.

It is an object of this invention to provide a bleach bath which will not be subject to one or more of the above disadvantages.

It is a further object of this invention to provide a bleach bath which minimizes or prevents the formation of blue dye buildup on color films and color papers.

It is still another object of this invention to provide a bleach bath for use in cine machine processing which prevents the buildup of blue dye formation on the processed film and/ or reduces the corrosion of the rollers used to transport the film.

Other objections and advantages of this invention will be apparent from the following description.

The attainment of the above objects is made possible by this invention which comprises the provision of improved processing solutions for color materials, said solutions containing an alkali metal ferricyanide, an alkali metal fluoride and a salt selected from the group consisting of potassium bromide, sodium bromide, potassium chloride, sodium chloride, and mixtures thereof.

"United States Patent 0 3,806,343 Patented Apr. 23, 1974 ice Our experiments have shown that alkali metal fluorides, preferably sodium or potassium fluoride, when used in conventional bleach formulations result in processed color films and color paper which are free from blue dye deposits of the type arising from the formation of Prussian Blue and Turnbull Blue.

Photographic bleach solutions which are used in the practice of this invention for the processing of color film contain, in aqueous solution, an alkali metal ferricyanide such as lithium, potassium or sodium ferricyanide as the oxidizing agent which converts the metallic silver formed during development into a silver salt which is soluble in silver halide solvents such as hypo (sodium thiosulfate). Typically such bleach solutions contain, in addition to the ferricyanide, a halogen containing compound, preferably potassium bromide, sodium bromide, potassium chloride, or sodium chloride, which converts the silver ferricyanide initially formed in the bleaching reaction into the less soluble silver chloride or silver bromide and thus impels the bleach reaction to completion. Prolonged use of the bleach solution also results in the presence of iodide salts therein which are generated from the processed materials.

The bleach reaction should be carried out at a preselected pH and consequently the ferricyanide bleach solutions contain buffering agents which maintain the desired pH even though small amounts of acids or alkali may be carried into the bleach by the film or paper. The pH of the bleach solution falls between the range of from 3 to 9, a pH between 4 and 6 being generally preferred. Among the more frequently used ingredients of such buffer mixtures are alkali metal phosphates such as disodium and monosodium phosphates, sodium stearate, sodium metaborate, Borax, sodium bisulfate, boric acid, citric acid, glacial acetic acid, and phthalic acid. Some of the ingredients in the buffer formulation additionally act as corrosion inhibitors and restrain the corrosive action of the ferricyanide bleach on metallic developing tanks, trays, rollers and the like. Additional corrosion inhibitors may be added, such as sodium nitrate, to the bleach formulation.

In many instances, an alkali metal ferrocyanide is included in the bleach formulation so as to give a tempering action to a freshly mixed bleach solution in order to stimulate the performance of a partly used bleach. The rate of bleaching depends on the oxidation-reduction potential which in turn is a function of pH and the relative ferro cyanide-ferricyanide concentration. No such oxidation-reduction potential can be established so long as ferricyanide is in the fresh solution, and no ferrocyanide has been formed as a result of the bleach action. The desired tempering action is achieved by adding to a fresh bleach solution specified amounts of ferrocyanide, thus establishing oxidation-reduction potentials which otherwise would be set up only after part of the ferricyanide had been reduced to ferrocyanide. The oxidation-reduction potential of a partially exhausted bleach solution can be increased and the effective lifetime of the solution can be extended by the addition of an alkali metal persulfate such as sodium or potassium persulfate.

Useful accelerators which accelerate the bleaching rate can be utilized. Among such accelerators are compounds such as monohydroxy alcohols and aliphatic ketones of the type described in US. Pat. 2,378,265, phenoxy alcohols of the type described in U .8. Pat. 2,419,900 and n-hexoxyethanol. Sequestering agents, such as sodium hexametaphosphate, also find active use in bleach formulations.

In achieving the objects of this invention a bleach processing solution comprising an alkali metal ferricyanide, an alkali metal fluoride, and a salt selected from the group consisting of potassium bromide, sodium bromide, potassium chloride and sodium chloride is utilized. The photographic bleach solution contemplated herein may optional- 1y contain buffer mixtures, corrosion inhibitors, alkali metal ferrocyanides and/ or alkali metal persulfates. Photographic bleach solutions which have been found to be effective may be compounded in the following proportions:

Grams Alkali metal ferricyanide 25-120 Salt selected from the group consisting of potassium bromide, sodium bromide, potassium chloride and sodium chloride 230 Alkali metal fluoride 0.5-10

and optionally Alkali metal ferrocyanide 2-12 Alkali metal persulfate 242 Water to make one liter.

The concentration of alkali metal fluoride in the bleachbath is not critical and may vary from about 0.5 to about 10 grams per liter of the bleaching solution, depending upon the processing equipment and conditions. While any of the alkali metal fluorides are contemplated, including lithium fluoride exceptionally good results are obtained by the utilization of potassium fluoride and sodium fluoride.

The following examples describe in detail the method and materials that comprise the present invention and are intended to be illustrative of said invention and not limiting thereof. All parts and proportions referred to herein and in the appended claims are by weight unless otherwise indicated.

EXAMPLE I A three-foot strip of 35 mm. multi-layer color film of the reversal type, containing color forms and prepared according to US. Pat. 2,179,228 and 2,179,239, was exposed and processed as follows.

The film was first developed for 14 minutes at 68 F. in a developer of the following composition:

Water to make one liter.

The developed film was short stopped for 2 minutes in a bath of the following composition:

Acetic acid Sodium acetate 20.0 Water to make one liter.

The material was then hardened for minutes in a 3% aqueous solution of potassium chrome alum and washed in water for three minutes.

The washed film was given a second exposure for 3 minutes to the light of a No. 1 photoflood lamp 30" away from the film and color developed for 15 minutes in a developer of the following composition:

Grams Sodium sulfite 2.0 p-Aminodiethylaniline-HC1 4.0

Sodium carbonate (monohydrate) 67.5 Potassium bromide 1.0 Water to make one liter.

The film was then short stopped for 1 minute, hardened for 3 minutes and washed in water for 5 minutes.

The film was then bleached for 10 minutes in an aqueous bleach solution of the following composition.

Grams Sodium hexametaphosphate 0.5 Potassium fluoride 1.0 Potassium ferricyanide 50.0 Sodium diacetate 12.0 Sodium bromide 15.0

Water to make one liter.

EXAMPLE 11 Example I was repeated with the exception that a bleach solution was used which had the following composition:

Sodium hexametaphosphate grams 2.0 Potassium ferricyanide do 25.0 Sodium bromide do 10.0 Sodium nitrate do 30.0 Sodium acetate do 15.0 Potassium fluoride do 2.0 Glacial acetic acid ml 1.5

Water to make one liter.

The film was free from residual blue stain after being bleached for only 5 minutes. A companion film which had been treated in an identical manner except for the fact that the bleached solution did not contain any potassium fluoride showed pronounced blue stain even after 5 minutes of bleaching.

This invention has been disclosed with respect to certain embodiments and it will be understood that modifications and variations thereof will become obvious to persons skilled in the art and are intended to be included within the spirit and purview of this application and the scope of the appended claims.

We claim:

1. A bleach solution for use in the process of color photography comprising an alkali ferricyanide, an alkali metal fluoride present in concentrations of from about 0.5 to 10 grams per liter of said bleach solution, and a salt selected from the group consisting of potassium bromide, sodium bromide, potassium chloride, sodium chloride and mixtures thereof.

2. A bleach solution as defined in claim 1 additionally containing an alkali metal ferrocyanide or an alkali metal persulfate.

3. A bleach solution as defined in claim 1 additionally containing a buffer compound.

4. A bleach solution as defined in claim 1 additionally containing a sequestering agent.

5. A bleach solution as defined in claim 1 additionally containing a corrosion inhibiting compound.

6. A bleach solution as defined in claim 1 additionally containing an iodide salt.

7. A bleach solution as defined in claim 1 wherein the alkali metal fluoride is potassium fluoride.

8. A bleach solution as defined in claim 1 wherein the alkali metal fluoride is sodium fluoride.

9. In a process of exposing and developing an exposed silver halide element comprising a method of removing silver from color film or paper containing dyestuff images, the improvement which comprises subjecting said film or paper to the action of a bleach solution as defined in claim 1.

6 References Cited UNITED STATES PATENTS 7/1962 Johnson 9660 R 12/1972 Mowrey et a1 96--60 BF US. Cl. X.R. 

